Notwithstanding that a wide variety of changeable ratio drive transmissions have been devised, the need for new and for improved structures of that kind has not been satisfied. Just as a wide variety of applications has created needs for fastening devices of widely different form, so, too, has a wide variety of practical applications created needs for many kinds and forms of variable ratio and adjustable ratio mechanical motion transmission systems, and the needs continue. Among them is a requirement for an adjustable ratio drive structure that can be packaged in minimum width, in which the ratio change can be accomplished in small incremental steps, which has relatively high transmission efficiency, and the ratio of which can be changed during drive operation.
There are a variety of applications for a device with those attributes. By way of example, it is that very list of attributes that is required in an adjustable ratio drive system for bicycles and small motor bikes.